The present invention relates generally to the field of dyes useful in image recording.
Kawamura et al. in U.S. Pat. No. 4,283,475 discloses a 2,6-di-t-butyl-4-[5-(2,6-di-t-butyl-4H-thiopyran-4-ylidene)penta-1,3-dienyl]thiopyrylium salts, and a process for production thereof. In particular, Kawamura et al. disclose 2,6-di-tert-butylthiopyrylium pentamethine hexafluorophosphate dye, as shown immediately below and identified as Compound (I), and variations of that dye. The variations alter the letter A from hydrogen to various other compounds disclosed in the ""475 patent. 
The thiopyrylium pentamethine dye of compound (I) has properties that make it a useful laser dye. For example, it has an absorption maximum of 822 nm in dichloromethane. This wavelength is compatible with gallium-arsenide diode lasers and other light sources emitting near 830 nm. Compound (I) also has an extinction coefficient in dichloromethane of 384,000 Mxe2x88x921cmxe2x88x921 at the absorption maximum and displays little crystallization in coated formats. These properties make compound (I) and variations thereof an ideal material for use as the heat-generating element in coated formats for thermal imaging, lithography, optical recording, and related imaging applications. Accordingly, compound (I) and its variations thereof are desired. The process to make these salts is set forth by Kawamura et al. In particular, Kawamura et al. disclose that the process is as follows: xe2x80x9cCompound (i) [as shown immediately below] is heated in the presence of phosphorus pentasulfide at Step (1) . . . to obtain compound (ii). The reaction product, Compound (ii) is then reacted with alkali hydrosulfide such as potassium hydrosulfide in a solvent at a temperature between 50xc2x0 C. to 200xc2x0 C. in an atmosphere of an inert and oxygen-free gas such as N2, CO2, and argon gas (Step 2) to produce compound (iii). The solvent used at Step 2 is water-free and non aqueous solvent having at least 20 of dielectric constant and at least 2 of dipole moment, for example, hexamethyl phosphoric triamide, dimethylsulfoxide, N,N-dimethylformamide or N-methylpyrrolidone. The alkali sulfide or alkali hydrosulfide used is 1 to 30 moles, preferably 3 to 20 moles, per 1 mole of compound (ii). Compound (iii) is then reacted with an alkylating agent at Step 3 to obtain compound (iv) which is then hydrolyzed to form compound (v) [Step 4]. The reaction temperature at Step (3) is xe2x88x9210xc2x0 C. to 200xc2x0 C., preferably 40xc2x0 C. to 100xc2x0 C. and the reaction time is 30 minutes to 2 hours. In formula (iv), R4 is an alkyl or substituted alkyl group derived from the alkylating agent. Compound (v) is subjected to the action of a Grignard reagent at a temperature of xe2x88x9220xc2x0 C. to 25xc2x0 C. for 30 to 90 minutes in a solvent and in a nonoxidizing atmosphere and then treated with an acid to form compound (II) (Step 5).xe2x80x9d
Compound (II) is known as 2,6,-di-t-butyl-4-methylthiopyrylium salt. To obtain the desired 2,6-di-t-butyl-4-[5-(2,6-di-t-butyl-4H-thiopyran-4-ylidene)penta-1,3-dienyl]thiopyrylium salts and in particular 2,6-di-tert-butylthiopyrylium pentamethine hexafluorophosphate, compound (II) is reacted with a 1-phenylamino-3-phenylimino-1-propene, as shown immediately below and identified as compound (III), or a salt of the compound (III) with an acid. 
The ""457 patent disclosed that the xe2x80x9cpreferred examples of the compound of formula (III) are 1-phenylamino-3-phenylimino-1-propene, 2-benzyl-1-phenylamino-3-phenylimino-1-propene, 2-phenyl-1-phenylamino-3-phenylimino-1-propene, 2-bromo- or 2-chloro-1-phenylamino-3-phenylimino-1-propene, and 2-ethyl-1-phenylamino-3-phenylimino-1-propene.
The acid forming a salt with the compound (III) is an acid having a pKa generally not more than 4, preferably not more than 1, and includes, for example, hydrochloric acid, hydrobromic acid and sulfuric acid.
The reaction of compounds (II) and (III) is carried out either in a carboxylic acid anhydride or in an amine. When the reaction is carried out in the carboxylic acid anhydride, the carboxylic acid anhydride contributes to the reaction system as an aniline-eliminating agent. As a carboxylic acid anhydride an aliphatic carboxylic acid anhydride containing 4 to 16 carbon atoms and which may be substituted with one or more substituents, may be used. The substituents include halogen atoms, such as fluorine and chlorine. Specific examples of the carboxylic acid anhydride include acetic acid anhydride, propionic acid anhydride and trifluoro acetic acid anhydride. In order to dissolve the reaction materials, there may be added an auxiliary solvent which does not react with the raw materials, the carboxylic acid anhydride, the base described hereinafter and the reaction product in the reaction system, such as acetic acid or nitrobenzene. This reaction requires the presence of a base. The base is generally an organic base, for example alkali metal acetates such as sodium acetate or potassium acetate; alkylamines, preferably primary amines having 1 to 10 carbon atoms, secondary amines having 2 to 20 carbon atoms total or tertiary amines having 3 to 30 carbon atoms; aromatic amines; and nitrogen-containing aromatic amines. Specific examples are triethylamine, piperidine, aniline, dimethylaniline, pyridine, and quinoline.
The amount of the base used is 0.2 to 100 moles, preferably 0.5 to 20 moles, per mole of the 2,6-di-t-butyl-4-methylthiopyrylium salt. The weight ratio of the carboxylic acid anhydride to the 2,6-di-t-butyl-4-methylthiopyrylium salt is 0.1-100:1, preferably 1-50:1.
When the reaction is carried out in an amine, an auxiliary solvent such as acetic acid or nitro-benzene may likewise be added. The amine used in this reaction may be the same as those exemplified above as the base. The amount of amine is generally about 0.5 to 200 moles, preferably 1 to 100 moles per mole of the 2,6-di-t-butyl-4-methylthiopyrylium salt.
This process is generally carried out at about 50xc2x0 to 200xc2x0 C., preferably 80xc2x0 to 140xc2x0 C. The amounts of compounds (II) and (III) may be stoichiometric. Generally, about 0.3 to 1 mole of the 1-phenylamino-3-phenylimino-1-propene is used per mole of the 2,6-di-t-butyl-4-methylthiopyrylium salt. The reaction time varies depending upon the reaction temperature, the type of the solvent, etc., but is generally 1 minute to 1 hour.xe2x80x9d
This process, however, is not economically viable because the overall yield of the critical compound (II) for the formation of compound (I) is below 30%, see synthesis example for compound (II) at columns 11 and 12 of the ""475 patent. Accordingly, there is a need to make compound (II) at significantly higher overall yields to make compound (I) and variations thereof economically viable. This invention solves this problem.
The present invention provides a novel method for the synthesis of an intermediate dye product having the following formula: 
wherein
L is S, Te, or Se;
R1 and R2 are either the same or different aryl or alkyl compounds;
R3 is hydrogen or a short chain alkyl group; and
Z is an anion.
The process to formulate this intermediate compound entails reacting an R1-acetylene compound with an R2-acetylene compound (compounds A) into an enol ether compound with the R1 and/or R2 constituents (compound D). And from compound D, it forms into an intermediate dye compound having an L-based cyclic ring with the R1 and/or R2 constituents (compound F). With compound F the desired dye can be made with a greater overall yield for mass production. 
The present invention describes the synthesis of an intermediate dye compound (identified above as compound F) from an acetylene product (identified above as compound A). Compound F has the following formula: 
wherein
L is S, Te, or Se;
R1 and R2 are either the same or different aryl or alkyl compounds;
R3 is hydrogen or a short chain alkyl group; and
Z is an anion.
In particular, R1 and R2 are aryl, and/or linear or branched alkyl groups having 1 to 15 carbon atoms, preferably 1 to 5 carbon atoms. Examples of such groups include, and are not limited to, methyl, ethyl, isopropyl, t-butyl, pentyl groups, phenyl, tolyl, ethylphenyl, naphthyl and variations thereof. The variations may be substituted with other aryl groups having (a) 6 to 15 carbon atoms, preferably 9 to 13 carbon atoms such as phenyl, tolyl, ethylphenyl and naphthyl groups; (b) halogen atoms, that is chlorine, bromine, fluorine and iodine; and (c) alkoxy groups having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, such as a methoxy group.
Also the anion identified as Z can be a single atomic ion or atomic grouping ions composed of a plurality of atoms which have a negative charge. Anions of strong acids represented by HZ and having a pKa of not more than 5, especially not more than 2, are preferred for easy synthesis of the thiopyrylium salts. Specific examples of the anions are single atomic ions such as halogen anions, e.g. fluoride, chloride, bromide and iodide ions; and ionic groups, for example organic anions such as trifluoroacetate, trichloroacetate and p-toluenesulfonate ions, and inorganic anions such as perchlorate, periodate, tetrachloroaluminate, trichloroferrate (II), tetrafluoroborate, hexafluorophosphate, sulfate, hydrogensulfate and nitrate ions. Divalent anions are interpreted, as a matter of formality, such that 1/2 of such an anion represents a monovalent anion.
The process of synthesis of compound F is as follows: 
In principle, compound E, which would be thiopyranone if L were Sulfur, should be readily prepared from diynone, compound C, by the addition of hydrogen sulfide. However, as shown below, the addition of hydrogen sulfide gas to ethanol solutions of compound C generate mixtures of thiopyranone, compound E, and dihydrothiophene, compound G, with compound G being the major product. The separation of compounds E and G requires a chromatographic separation. 
The formation of compound G can be avoided completely by converting the compound C to a mixture of enol ethers (compound D) by the careful addition of ethanol across one of the triple bonds of compound C to a mixture of enol ethers. That careful addition of ethanol across one of the triple bonds of compound C is an 0.07 M sodium ethoxide in ethanol. Addition of sodium sulfide or sodium hydrosulfide to the enol ethers, compound D, (both stereoisomers are observed in an 84:16 ratio) gives thiopyranone (compound E), if L is Sulfur, as the only heterocyclic product, which is isolated as a crystalline product from the crude reaction mixture.
Alternatively, the addition of sodium selenopyrylium or sodium telluropyrylium generates a compound D wherein the element L is respectively selenopyrylium or telluropyrylium.
Compound E then converts to compound F. This conversion occurs after compound F is (1) dissolved in tetrahydrofuran (THF), (2) mixed with methylmagnesium bromide in ether, and (3) then the desired anionic solution HZ is added.
Once compound F is formed, the desired dye can be fabricated, in this case compound H is illustrated below as 2,6-R1,R2 thiopyrylium pentamethine with an anion, Z: 
The process to generate compound H as 2,6-R1,R2 thiopyrylium pentamethine with an anion, uses triethylamine and 1,1,3,3-tetramethoxypropane to form the pentamethine unit. Obviously, the methine chain between the pyrylium groups can have various chain lengths. In particular, the range of the methine chain can be from 1 to 5 carbons depending on which product is used to form the compound H.
The standard recipe for use of 1,1,3,3-tetramethoxypropane with active methyl compounds such as 4-methylthiopyrylium salt (compound F if L is Sulfur) is to use an alcohol as solvent (typically ethanol) with acid catalysis (5% hydrochloric acid). Use of hydrochloric acid catalysis in ethanol gave  less than 5% isolated yield of compound H. Alternatively, similar reactions with bis anilinium salts of 1,3-propanedial as electrophile use sodium acetate in a mixed solvent of acetic acid and acetic anhydride to affect deprotonation of the 4-methylthiopyrylium salt and addition to the electrophile to form a polymethine dye. We found unexpectedly that addition of triethylamine to the 4-methylthiopyrylium salt (compound F) in the sodium acetate/acetic acid/acetic anhydride mixture gives appropriate buffering to eliminate methanol from the 1,1,3,3-tetramethoxypropane to generate the electrophile in situ. Isolated yields of compound F were 94%. Using sodium acetate as the only base gave  less than 5% yield of dye as did the use of pyridine as base.
This procedure is applicable to the synthesis of other thiopyrylium mono, di, tri, buta, or pentamethine dyes starting with appropriate acetylenic starting materials. Selenopyrylium and telluropyrylium analogs of these dyes can be prepared as well.